将多个项目作为一个项目插入到db中

I am trying to accept multiple items from a form and when they reach php for processing, split the items and treat them as seperate items to insert into db. What is happening at the moment, is that the items are being inserted into the db as one item. For example, I enter item1,item2,item3. This is being inserted into the db in one column. all three items in one column. How can I correct my code to have each item in there own column. Many thanks

php page

foreach($_POST['BRVbrtrv_boxnumber'] as $i=>$value){
$_POST['BRVbrtrv_boxnumber'][$i]=mysql_real_escape_string($value);
}

$boxnumber = implode( ',', $_POST['BRVbrtrv_boxnumber']);

$query = 'INSERT INTO `act` (`service`, `activity`, `department`, `company`,  `address`, `user`, `item`, `destroydate`, `date`, `new`)
         VALUES (\''.$service.'\', \''.$activity.'\', \''.$department.'\', \''.$company.'\', \''.$address.'\', \''.$authorised.'\', \''.strtoupper($boxnumber).'\', NULL, NOW(), \''.$new.'\');';
mysql_query($query) or die('Error, query failed');

jquery input

for(var i = 0;i < $(this).val();i++) {
$("#BRVbrtrv_boxnumber").append('<div data-role="fieldcontain"><label for="BRVbrtrv_boxnumber" class="ui-input-text">Enter box ' + (i + 1) + ' number:</label><input type="text" name="BRVbrtrv_boxnumber['+i+']" id="BRVbrtrv_boxnumber['+i+']" class="BRV_boxnumber ui-input-text ui-body-null ui-corner-all ui-shadow-inset ui-body-c" /></div>')
}

json output

boxnumber: "rff,tgg" <- this is correct values for 2 items that I input

+++UPDATE+++

    foreach($_POST['BRVbrtrv_boxnumber'] as $i=>$value){
            $_POST['BRVbrtrv_boxnumber'][$i]= strtoupper( mysql_real_escape_string($value) );
    }

    foreach( $_POST['BRVbrtrv_boxnumber'] as $k => $item_name ){

    header("Expires: Mon, 26 Jul 1997 05:00:00 GMT" );
    header("Last-Modified: " . gmdate( "D, d M Y H:i:s" ) . "GMT" );
    header("Cache-Control: no-cache, must-revalidate" );
    header("Pragma: no-cache" );
    header("Content-type: application/json");
    $json = "";
    if(empty($service)) {
    $json .= "{\"ErrorService\": \"ERROR: You mest select a service level\"}";
     }

    else
    if($department=="Choose Department") {
    $json .= "{\"ErrorService\": \"ERROR: You must select a department\"}";
     }

    else
    if($address=="Choose Address") {
    $json .= "{\"ErrorService\": \"ERROR: You must select a retrieval address\"}";
     }

    else
    if(empty($item_name)) {
    $json .= "{\"ErrorService\": \"ERROR: You must enter a box for retrieval\"}";
     }

    else
    {
    $json .= "{
";
    $json .= "\"boxnumber\": \"".$item_name."\",
";
    $json .= "\"boxcount\": \"".$boxcount."\"
";
    $json .= "}
";
    }
 }
foreach($_POST['BRVbrtrv_boxnumber'] as $i=>$value){
        $_POST['BRVbrtrv_boxnumber'][$i]= strtoupper( mysql_real_escape_string($value) );
}

foreach( $_POST['BRVbrtrv_boxnumber'] as $k => $item_name )
{

    $query = 'INSERT INTO `act` (`service`, `activity`, `department`, `company`,  
                                 `address`,  `user`, `item`, `destroydate`, `date`
                                 ,`new`)
   VALUES (\''.$service.'\', \''.$activity.'\', \''.$department.'\', \''.$company.'\',  \''.$address.'\', \''.$authorised.'\', \''.$item_name.'\', NULL, NOW(), \''.$new.'\');';
mysql_query($query) or die('Error, query failed');
} 

I think you need to explode the $_POST['BRVbrtrv_boxnumber'], and then have a for loop processing the returned array, in which you do your insert.